DNA is the genetic material of all living things, except for viruses, most of which have genomes that are RNA—not DNA. Further, the majority of viral RNA genomes are single-stranded (ss) rather than duplex chains. The simplest of these ssRNA viruses, whether infecting bacteria, plants, or animals, involve a single copy of their genome, protected (packaged) by a single-molecule-thick spherical shell (capsid) of protein, which is typically smaller than 25 nm in radius. The small size is advantageous for minimizing the amount of ...